Hermione Granger tricked Umbridge into believing Dumbledore had hid a secret weapon of some sort in the Forbidden Forest (OP32). When the self-appointed Headmistress followed Hermione and Harry into the Forest, they were ambushed by centaurs. The creatures eventually led Umbridge away, but the instrumental interference of Grawp prevented them from touching the two students (OP33).

The two Gryffindors, joined by other members of the D.A., then made their way to the Ministry itself (OP34), where the Battle of the Department of Mysteries occurred (OP35) and unmistakingly revealed Lord Voldemort's return to the wizarding population (OP36). This eventually forced Fudge to resign (HBP1), and Dumbledore was of course reinstated in all his former positions and titles.